Figure 1

Your lungs, one of the largest organs of the body, are part of the respiratory system. They are critical to keeping you alive, and they need to be able to expand so they are protected by the strong yet flexible bones of your rib cage. One lung is usually larger than the other.

The purpose of the respiratory system is to replenish the oxygen in your blood and get rid of your blood's carbon dioxide through a process called respiration. When you breathe in, air travels from your nose or mouth down through your windpipe (trachea) to the bottom, then it branches into the main bronchial tubes. The right tube leads into the right lung and the left tube into the left lung. Each bronchial tube continues to branch out into smaller and narrower tubes. The smallest tubes in the lungs are called bronchioles. At the end of each bronchiole are tiny air sacs known as alveoli. There are approximately 300 million alveoli in the lungs, and it is here that the vital exchange of oxygen and carbon dioxide occurs. When you breathe out, the flow of air follows the same path in reverse and air is exhaled through your nose or mouth. Sometimes, normal respiration is hampered by a respiratory problem, such as asthma or chronic obstructive pulmonary disease (COPD).